This invention relates generally to a control unit for a resin bed type water softener and more particularly to an improved microcomputer-based control unit for a resin bed water softener which continually monitors the resin bed capacity and adjusts for the additional capacity created when a partially exhausted resin bed is regenerated with the amount of regenerant normally required by a fully exhausted resin bed.
The most common type of water softener is the ion exchange resin-type softener having a vertically disposed tank which holds a bed of resin through which the hard water is passed to remove undesirable minerals and other impurities. The capacity of the resin bed to absorb minerals and impurities is finite and it is thus necessary to periodically recharge or regenerate the resin bed with a regenerant, typically a brine solution, by causing the brine solution to flow from one end of the tank to the other so as to restore the capacity of the resin bed for further water treatment.
The two types of processes commonly employed to regenerate a resin bed water softener are co-current regeneration and counter-current regeneration. Co-current regeneration is accomplished by causing the regenerant fluid (brine solution) to flow in the same direction as the normal or service flow of the incoming water through the resin bed. Typically, the service flow is directed downwardly against the resin bed to keep the resin bed compacted. In contrast, counter current regeneration is achieved by causing the regenerant fluid to flow upwardly, at a low velocity, through the resin bed to maintain the resin bed in a compacted mass. As will be understood by those skilled in the art, the downward and upward flow of regenerant during co-current and counter-current regeneration, respectively, could be reversed if other means were employed to maintain a compacted resin bed.
During the normal or service flow of water through the resin bed, the hard water entering the flow inlet tends to first exhaust the resin nearest the inlet so that the resin within the tank tends to stratify into an exhausted section adjacent to the service inlet and an undiminished or unexhausted section adjacent to the service outlet. The unexhausted portion of the resin bed is separated from the exhausted section by a relatively narrow band of resin comprised of a mixture of exhausted and unexhausted resin particles. During a co-current regeneration, the regenerant, which flows in the same direction as the service flow, first contacts the exhausted resin causing the metallic or hardness ions that were previously exchanged during the service flow of water, to be released from the resin and replaced with the ions of the regenerant. Before the hardness ions may be flushed from the resin tank, the hardness ions must pass through the unexhausted resin adjacent to the outlet. However, as the hardness ions pass through the unexhausted resin, the hardness or metallic ions are exchanged with the unexhausted resin as occurs normally during the softening process. Thus, the previously unexhausted resin becomes exhausted. Therefore, the regenerant fluid contacts only the exhausted resin as it flows toward the outlet and, as a result, there is no difference during a co-current regeneration between when the resin bed is partially exhausted or when the bed is totally exhausted. The capacity of the resin bed remains the same regardless of whether the bed is partially exhausted or fully exhausted.
During a counter-current regeneration, the regenerant flows in a direction opposite to that of the service flow and thus enters the resin bed through what was the service flow outlet and first contacts the unexhausted resin. Since the unexhausted resin contains no metallic or hardness ions, the regenerant generally remains unaffected as it flows through the unexhausted resin until the regenerant passes into the exhausted resin portion where ion exchange does occur, causing the regeneration of the exhausted resin. As a consequence, the released hardness ions pass only through the exhausted resin without further exchange as they are flushed from the resin bed. The counter-flow of regenerant during counter-current regeneration results in an effectively increased amount of regenerant, as measured in pounds, that is available to regenerate the exhausted resin, as measured in cubic feet, of a partially exhausted resin bed in comparison to a completely exhausted resin bed. This may be seen from the following example. Assuming the amount of regenerant used during each regeneration is set at 6 pounds of brine (NaCl) solution and the volume of resin in the tank is 1 cubic foot, then, the regenerant level applied to completely exhausted bed will be given as follows: ##EQU1##
When the resin bed is only two-thirds exhausted (1/3 capacity remaining) then, assuming that the regenerant only acts upon the exhausted portion of the resin bed, the regenerant level applied to the exhausted resin will be given by ##EQU2## Thus, the effective regenerant level applied to the exhausted portion of the resin bed is much greater than the regenerant level applied to the bed where the bed completely exhausted.
It is well known to those skilled in the art that the additional resin bed capacity created upon regeneration of a partially exhausted resin bed is a function of the regenerant level. For example, the resultant capacity-regenerant level relationship for a common resin, such as IONAC type C-253 resin, manufactured by Sybron Corporation, Birmingham, N.J., is illustrated below in Table 1.
TABLE I ______________________________________ Regenerant level Capacity (lb. of NaCl/cubic feet) (grains of CaCO.sub.3 /cubic foot) ______________________________________ 6 20,000 9 27,500 12 30,000 15 31,500 ______________________________________
As may be appreciated from examination of Table I, the capacity does not increase in direct proportion to the regenerant level.
Using the capacity data set forth in Table I, the increase in capacity for the previous example may be calculated in the following manner. If the one cubic foot resin bed is completely exhausted, and the regenerant level is 6 lbs./ft..sup.3, and the resultant capacity will be given by EQU Resultant Capacity=1 ft..sup.3 .times.20,000 grains/ft..sup.3 =20,000 grains (3)
Assuming that 2/3 of the resin bed is exhausted and 1/3 remains unexhausted, the capacity of the unexhausted resin bed, assuming that it had been completely regenerated during a previous interval with a regenerant level of 6 lb./ft..sup.3, will be given by EQU Resultant Capacity=1/3 ft..sup.3 .times.20,000 grains/ft..sup.3 =6,666 grains (4)
The resultant capacity of the exhausted resin, when regenerated with an effective regenerant level of 9 lb./ft..sup.3 as determined previously by Equation (2) will be given as follows EQU Resultant Capacity=2/3 ft..sup.3 .times.27,500 grains/ft..sup.3 =18,333 grains (5)
The total capacity is the sum of the capacity of the unexhausted 1/3 portion of the bed (6,666 grains) plus the capacity resulting from regeneration of the 2/3 portion of the exhausted bed with a regenerant level of 9 lb./ft.sup.3 (18,333 grains) as may be seen from Equation 5 which is EQU Total Capacity=6,666+18,333=25,000 grains (6)
The capacity increase will be given by EQU Capacity Increase=25,000-20,000=5,000 grains
As may be appreciated from Equation (6), a 25% capacity increase is obtained. If the hardness of the incoming water is 20 grains per gallon, then the volumetric increase in capacity would be given by ##EQU3## The foregoing example thus indicates that a significant amount of additional capacity may be obtained merely by recognizing the increased capacity resulting from regeneration of the exhausted portion of the resin bed with a regenerant level which is effectively greater than that employed to regenerate a completely exhausted bed.
Present day water softener controls, and even the advanced microcomputer-based water softener control disclosed in the now allowed U.S. patent application Ser. No. 412,279 now U.S. Pat. No. 4,426,294 for "Microcomputer Controlled Demand/Scheduled Water Softener" filed by J. David Seal on Aug. 27, 1982, and assigned to the assignee of the present invention, do not recognize and evaluate the additional capacity resulting from regeneration of the exhausted portion of the resin bed with the increased regenerant level. If a control could recognize and evaluate the additional capacity, then the number of regenerations would be reduced without increasing the possibility of delivering unsoftened water. By reducing the number of regenerations, a savings of regenerant and water would be effected.
It is an object of the present invention to provide an improved water softener control unit which utilizes a microcomputer to control water softener resin bed regeneration.
It is another object of the present invention to provide an improved microcomputer-based water softener control unit which controls water softener resin bed regeneration in accordance with the remaining capacity of the water softener resin bed to treat water.
It is yet another object of the present invention to provide an improved microcomputer-based water softener control unit which initiates water softener resin bed regeneration when the remaining resin bed capacity as determined from the actual soft water consumption is less than a reserve value calculated in accordance with the actual soft water consumption so that regeneration occurs only when necessary, thereby achieving a savings of regenerant and water.
It is yet another object of the present invention to provide an improved microcomputer-based water softener control which recognizes and adjusts for the increased capacity created when a partly exhausted resin bed is regenerated. The control initiates regeneration based on the additional capacity value so as to achieve an even greater savings of regenerant and water.